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    <title>Document</title>
    <script src="./js/jquery.js"></script>
    <script src="./js/idnex.js"></script>
    <style type="text/css">
        * {
            margin: 0;
            padding: 0;
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        ul {
            list-style: none;
        }

        .wrap {
            width: 330px;
            height: 30px;
            margin: 100px auto 0;
            padding-left: 10px;
            background-image: url(imgs/bg.jpg);
        }

        .wrap li {
            background-image: url(imgs/libg.jpg);
        }

        .wrap>ul>li {
            float: left;
            margin-right: 10px;
            position: relative;
        }

        .wrap a {
            display: block;
            height: 30px;
            width: 100px;
            text-decoration: none;
            color: #000;
            line-height: 30px;
            text-align: center;
        }

        .wrap li ul {
            position: absolute;
            top: 30px;
            display: none;
        }
    </style>
</head>
<body>
    <div class="wrap">
        <ul>
            <li>
                <a href="javascript:void(0);">一级菜单1</a>
                <ul>
                    <li><a href="javascript:void(0);">二级菜单1</a></li>
                    <li><a href="javascript:void(0);">二级菜单2</a></li>
                    <li><a href="javascript:void(0);">二级菜单3</a></li>
                </ul>
            </li>
            <li>
                <a href="javascript:void(0);">一级菜单2</a>
                <ul>
                    <li><a href="javascript:void(0);">二级菜单1</a></li>
                    <li><a href="javascript:void(0);">二级菜单2</a></li>
                    <li><a href="javascript:void(0);">二级菜单3</a></li>
                </ul>
            </li>
            <li>
                <a href="javascript:void(0);">一级菜单3</a>
                <ul>
                    <li><a href="javascript:void(0);">二级菜单1</a></li>
                    <li><a href="javascript:void(0);">二级菜单2</a></li>
                    <li><a href="javascript:void(0);">二级菜单3</a></li>
                </ul>
            </li>
        </ul>
</body>
</html>